Public awareness and concern about harmful algal blooms – United States, 2020

Harmful algal blooms result from rapid growth of harmful algae or cyanobacteria in water. These blooms occur throughout the United States in freshwater bodies, such as lakes and rivers, and marine waters, such as oceans and bays (Lopez et al. 2008; Loftin et al. 2016; Anderson et al. 2021). Harmful algal blooms cause mild to life-threatening human and animal illnesses and negatively impact environments and economies (Adams et al. 2018; Roberts et al. 2020). They are a public health threat that can be exacerbated by climate change effects such as warming waters and nutrient pollution (Gobler 2020; Roberts et al. 2020). Public awareness of harmful algal blooms and their health risks is important for illness prevention. However, limited data exist describing public awareness and concern regarding harmful algal blooms. Previous research indicates moderate to high awareness of harmful algal blooms and varying levels of concern about their impacts among local communities and specific groups, such as anglers, farmers, and beachgoers (Smith et al. 2014; Sohngen et al. 2015; Cahyanto & Liu-Lastres 2020; Shr & Zhang 2021). However, national data to estimate public awareness and concern about the health impacts of harmful algal blooms have not been previously collected. The purpose of this study was to: (1) assess U.S. adult awareness nationally of human and animal health impacts of harmful algal blooms and concern about health and economic impacts, and (2) characterize differences in awareness and concern by respondent demographic characteristics. Understanding awareness and concerns about harmful algal blooms among different groups can help public health practitioners tailor illness prevention messages for specific audiences.

We used Porter Novelli's Fall 2020 ConsumerStyles survey, which was administered between September 24 and October 10, 2020. The online survey was sent to a nationally representative sample of 4,548 participants 18 years or older who were part of the market research and consulting firm Ipsos' KnowledgePanel (Porter Novelli 2023). Panel members were recruited randomly by mail using address-based probability-based sampling and were provided with a laptop or tablet computer and Internet access if needed. The first multiple choice question asked whether participants had heard that harmful algal blooms can be unsafe for people and various animals¹. The second multiple choice question asked participants if they were concerned about harmful algal blooms affecting human health, pet health, or the economy.²

To adjust for sampling design and nonresponse, survey data were weighted to be representative of the U.S. adult population based on the Census' Current Population Survey benchmarks for sex, age, race, ethnicity, education, U.S. census region, household income, household size, and metropolitan area status. The data file provided by Porter Novelli did not contain personally identifying information. This activity was deemed not to be research as defined in 45 CFR 46.102(e) and IRB review was not required. We used SAS (version 9.4; SAS Institute) to conduct descriptive analyses for all responses and by specific demographic characteristics, such as region, race, ethnicity, education level, and income. We used Chi-square tests to compare two categories to each other; statistical significance was determined with p-values of <0.05 differences between categories within a variable.

A total of 3,625 people (80% response rate) completed the Fall 2020 ConsumerStyles survey. Nearly three-fifths (59%) of respondents were aware that harmful algal blooms can threaten human or animal health (Table 1). Awareness was higher for human health impacts, including that harmful algal blooms are not safe to enter or swim in (49%) and can make people sick (48%). Fewer respondents were aware of animal health impacts, including that harmful algal blooms can kill fish or other wildlife (42%), pets (31%), and livestock (22%). Awareness of at least one human or animal health impact varied by self-reported health status and was associated with older age, White race, non-Hispanic ethnicity, higher education level, not having a child in the household, and higher income. Although no significant differences in awareness were observed between coastal and inland state residents, there were differences by census region. New England residents had the highest overall awareness about health impacts.

Nearly a third (32%) of respondents were concerned about at least one health or economic impact of harmful algal blooms (Table 2). Participants were most concerned about harmful algal blooms making lake or ocean beaches unsafe (25%). They were less concerned about harmful algal blooms harming the economy (tourism or fishing) (19%); making them or their family sick (17%); and making their pets sick (11%). Being concerned with at least one impact varied by census region and was associated with higher education levels and living in a coastal state.

Unfamiliarity and lack of concern were evident among the remaining participants: 38% were unfamiliar with harmful algal blooms and 30% were not concerned about their impact on health or the economy. Not being familiar with harmful algal blooms varied by census region and self-reported health status, and was associated with female sex, non-White race, Hispanic ethnicity, lower education level, and lower income. Not being concerned with any impacts varied by education and income, and was associated with male sex, White race, non-Hispanic ethnicity, living in the Mountain region, and living in an inland state.

Although harmful algal blooms occur throughout the United States and are increasing in some regions (Lopez et al. 2008; Gobler 2020; Smucker et al. 2021), more than a third of the Porter Novelli survey respondents were unfamiliar with them. This is consistent with previous analyses that found 20% of Iowans and 40% of Louisiana fishermen were unfamiliar with harmful algal blooms (Smith et al. 2014; Shr & Zhang 2021). This result suggests U.S. adults nationally are less familiar with harmful algal blooms than groups who spend time near water bodies with recorded harmful algal blooms; previous analyses found only 4% of Lake Erie anglers and 10% of instate visitors to Florida beaches were unfamiliar with harmful algal blooms (Sohngen et al. 2015; Cahyanto & Liu-Lastres 2020).

Results showed discrepancies between public awareness and concerns related to harmful algal blooms nationally. Despite outreach by organizations across the U.S. about the health impacts of harmful algal blooms (Hardy et al. 2021), awareness was moderate (59%) and concern about these or related economic impacts was low (32%). Risk of exposure to harmful algal blooms may be greater for certain groups, including recreational and subsistence shellfish harvesters, people who use surface water drinking supplies, and people who spend time in or near water bodies (Gessner & Schloss 1996; Fleming et al. 2002; Lévesque et al. 2014; Backer et al. 2015; Solomon et al. 2022). However, risk of illness can depend on many factors – including geographical differences in harmful algal bloom occurrence, drinking water treatment methods, and individual characteristics such as pre-existing health conditions (Carmichael et al. 2001; Fleming et al. 2007; Westrick 2008; Loftin et al. 2016; Anderson et al. 2021) – and may be changing. Climate change effects are expected to increasingly favor the growth and toxicity of harmful algal blooms in more areas (Smucker et al. 2021; Merder et al. 2023), so awareness and concern among groups who were previously not impacted may become increasingly important for illness prevention. More effective public messaging about health risks may help increase awareness and concern among people who are likely to become ill from harmful algal blooms. Although more immediate efforts to communicate illness prevention messages can be tailored to higher-risk populations, a broader understanding of national awareness and concern can inform longer-term strategies for preparedness and response coordination at a national level.

Awareness and concern nationally varied by demographic characteristics of respondents. Harmful algal blooms are a complex phenomenon and communicating effectively about their risks can be challenging. Messages that are easy to understand and resonate with groups that reported less awareness of harmful algal blooms and associated impacts – including people with lower education and income levels, and those who identify as Hispanic or of a race other than White – may be particularly important when those groups are also at high risk of exposure. Similarly, understanding risk behaviors, perceived risk, and values of groups with low levels of concern about harmful algal blooms impacts – including males, Mountain region and inland state residents, those who identify as White and non-Hispanic, and have higher income and education levels – might help public health officials more effectively communicate with these groups to prevent illnesses.

Understanding regional variation in awareness and concern can also help officials prioritize and tailor harmful algal bloom messages in areas with frequent harmful algal blooms. More robust efforts to characterize groups at higher risk of illness and better understand health inequities between groups would help practitioners define priority audiences. Formative communication science research with priority audiences should be incorporated into efforts to develop effective public messaging about the risks of harmful algal blooms. Other researchers and practitioners have made similar recommendations (CRRC & NOAA 2023). Additionally, as groups at higher risk of illness are better defined, practitioners should focus messaging efforts on reaching people within these groups who report low awareness and concern about the health impacts of harmful algal blooms.

This report's findings are subject to at least five limitations. First, the data are self-reported so the accuracy of survey respondents' knowledge of health impacts cannot be verified. Second, survey responses reflect a single point in time and do not necessarily reflect changing levels of awareness or concern about harmful algal blooms. For example, awareness and concern about harmful algal blooms may have been depressed in 2020 due to a greater focus on the COVID-19 pandemic. However, participants completed the survey in early autumn, often a peak time for harmful algal bloom growth and media coverage, which may have reduced the effect of recall error. Third, as a descriptive analysis, the results cannot control for the effects of individual demographic groups. Fourth, although nationally representative, a small sample size relative to the U.S. population limits the extent to which differences between demographic groups (e.g., race) can be characterized or interpreted. Fifth, information about participant behaviors that could increase risk, such as swimming in water bodies or eating seafood, was not available. This information could help professionals evaluate these findings and tailor prevention messages for those at higher risk of illness.

This report describes the first nationally representative U.S. survey to estimate public awareness and concern about harmful algal blooms and their impacts. These findings support a continuing need to educate the public about harmful algal blooms and their impacts. They also highlight demographic and geographic differences that – paired with information about exposure risk – can inform future efforts. Public health messaging can be enhanced by incorporating information learned from evaluations of public awareness, behaviors, attitudes, and exposure risk related to harmful algal blooms.

Survey respondents; Fred Fridinger, Office of Communications, CDC; Deanne Weber, Porter Novelli Public Services.

Centers for Disease Control and Prevention purchased the survey data license from Porter Novelli.

All relevant data are included in the paper or its Supplementary Information.

The authors declare there is no conflict.